Filariasis is an important group of diseases affecting humans for which there is no adequate chemotherapy. Biochemical differences have now been shown to exist between the various species. It is proposed: 1) to continue biochemical investigations of the energy metabolisms of both adult and microfilarial forms of Litomosoides carinii, Dipetalonema viteae, Brugia pahangi and possibly Dirofilaria immitis; 2) to study the physiological function of the highly cristaeted mitochondria in the anaerobic, homolactate fermenters such as D. viteae and B. pahangi; 3) to examine the amino acid metabolism of these mitochondria; and 4) to study the modes of action of several antifilarial compounds, particularly levamisole and 4-isothiocyanato-4'-nitrodiphenylamine (CGP 4540). Standard isotope and enzyme techniques will be employed to elucidate and compare metabolic pathways. A similar approach in addition to EM autoradiography, and ultrastructural observations are proposed for the study of the effects of antifilarial agents.